Optical Observations of 3C 273 From 2000 to 2008

The quasar 3C 273 is one of the widely studied quasars that is also a selected target in our monitoring program. In this paper, we present the optical V, R, and I photometric observations done with the 1.56 m telescope at the Shanghai Astronomical Observatory from 2000 to 2008. Our monitoring results show 1118 sets of observations (258 sets for the V band, 414 sets for the R band, and 446 sets for the I band). The observations indicate that (1) the variations in the three bands are Delta *DV = 1.363 +/- 0.088 mag from V = 12.204 +/- 0.062 to V = 13.567 +/- 0.062, Delta *DR = 1.299 +/- 0.023 mag from R = 12.014 +/- 0.014 to R = 13.313 +/- 0.013, and Delta *DI = 1.041 +/- 0.088 mag from I = 11.628 +/- 0.046 to I = 12.669 +/- 0.075. Compared with the result by Toone, who presented the yearly averaged light curve during the period of 1980-2004 and found that the source shows a slow brightening with V = 12.95 in 1996-1997 to V = 12.5 in 2003-2004, our observations show that it is variable and both a state brighter than the yearly averaged brightness of V = 12.5 and a state fainter than the yearly averaged brightness of V = 12.95 were detected in our observing period. Intra-day variation timescales are from 13 minutes to 245 minutes. (2) The color indices are variable with V-R from -0.27 to 0.68, V - I from 0.11 to 1.14, and R - I from 0.14 to 0.86. The average values are V - R = 0.18 +/- 0.10, V - I = 0.64 +/- 0.14, and R - I = 0.46 +/- 0.11.